With the recent advances in small-incision cataract surgery, increased emphasis has been placed on developing soft, foldable materials suitable for use as intraocular lenses or other ophthalmic implants. Typically, these materials fall into one of three categories: hydrogels, silicones, and acrylics. The intraocular lens (IOL) industry has generally avoided many other materials due to the physical or chemical properties that make those materials unsuitable for use as IOLs. As an example, many materials do not exhibit the desired softness and/or ability to fold that is required when an IOL is folded, stretched and/or compressed for insertion into an eye through a cartridge tip that fits into a small incision in the eye.
Polystyrene is one material that has generally been avoided when forming IOLs. Polystyrene typically has a relatively high glass transition temperature (Tg). As such, polystyrene tends to be a hard plastic at human body temperature with little flexibility. This lack of flexibility causes polystyrene to be generally undesirable as an IOL material since it typically cannot be pushed through a small cartridge tip.
Although polystyrene lacks flexibility, it exhibits properties such as high strength, desirable refractive index and lack of biodegradability that are particularly desirable for IOLs. As such, it would be desirable to have a polystyrene material that provided enough flexibility that it could be injected into the eye as an IOL.
One common method of providing flexibility to polystyrene involves the incorporation of one or more flexible materials such as butadiene rubber with the polystyrene. Materials such as butadiene rubber are normally incompatible with polystyrene and cannot be mixed, however, addition of butadiene during the polymerization of polystyrene allows the butadiene to be chemically bonded with the polystyrene. The butadiene can be grafted to the polystyrene backbone or can be integrated into the backbone itself. Such structures are shown below:

The resultant styrene-butadiene (SBR) copolymers have excellent mechanical and thermal properties for use as IOLs. Such properties can allow the material to be folded and compressed for insertion through small inner diameters of injection cartridges.
These SBR polymer, however, do suffer from significant drawbacks that make them unsuitable for use as an IOL. SBR polymers include unsaturated carbon-carbon double bonds, which can make them prone to oxidation side reactions. Further, SBR polymers are prone to forming glistenings which can obstruct vision. Further yet, butadiene is a gas under ambient conditions and is therefore very difficult to process into an IOL.
In view of the above, it would be particularly desirable to create a polystyrene material that is suitable for use as an ophthalmic or otorhinolarygological device material and particularly suitable an IOL material.